1. Field of the Invention
The present invention relates to a method and apparatus for recording images and, more particularly, to such image recording method and apparatus which enable recording of an image on sheet material in such manner as to protect the recorded images against the degradation of image quality by dirt, for example.
2. Description of the Prior Art
In the art, various recording methods have been proposed to record images on sheet material. Among them, a thermal recording method has been widely admitted to be advantageous in respect of reliability and operability. Japanese Patent Application laid open Nos. 161946/1979 and 82676/1980 have disclosed a recording apparatus based on the principle of the thermal transfer recording method. With the recording apparatus, a common uncoated paper can be used as the recording medium. Furthermore, there are obtained recorded images having improved resolution. In this known apparatus, an image is recorded through two transfer steps, an intermediate transfer step and a final transfer step. At the intermediate transfer step, the surface of an intermediate transfer film is brought into contact with a portion of the solid ink layer of a transfer master. While keeping the contact, the ink layer is selectively heated by means of a heating element from the backside of the film so as to transfer an ink image onto the film. At the final transfer step, the ink image is transferred onto a sheet of common paper from the film.
Since the ink is heated through an intermediate transfer film, the amount of ink transferred onto the film is maintained nearly constant even when the solid ink layer on the transfer master has some irregularity in layer thickness. Therefore, there are obtained images of high resolution. This is an important advantage of the thermal transfer recording system mentioned above. Another advantage of the recording system is that as the recording medium there may be used not only any common papers but also any other media optionally selected.
The above image recording process comprising the steps of forming an image on an intermediate transfer film at first and then transferring the image onto a recording paper from the film may be applied to various recording systems other than the above described thermal recording system by suitably modifying the method of forming images on the intermediate transfer film.
However, in any case, the known image recording method involves some problems. Firstly, a periodical exchange of the intermediate transfer film is required because it is worn and damaged in use. Time and labour consumed for such maintenance work are by no means small. Secondly, it is difficult to increase the efficiency of image transfer from the intermediate transfer to the final recording material. There has not yet been proposed any effective solution to this problem.
The thermal recording method is a good method also for recording multi-color images or natural color images on sheet material. However, when sharp and clear color images are desired, the method according to the prior art is not satisfactory.